1. Field of the Invention
The present invention relates to a driving control apparatus for controlling the driving of a motor-driven compressor mounted on an automobile.
2. Description of the Related Art
A battery is utilized as an electric source to run an automobile such as an electric motorcar, and a travelling distance of the electric motorcar depends on a battery capacity. The battery is utilized to supply an electric power to not only a drive motor but also a motor-driven compressor which is utilized for air conditioning. Also, an electric generator is utilized to supply an electric source to the motor-driven compressor in the automobile such as a gasoline Car.
Therefore, an electric power supplied to the motor-driven compressor is controlled by a conventional driving control apparatus to prevent the motor-driven compressor from burning out. For example, a conventional driving control apparatus of a motor-driven compressor was laid open to public inspection under Provisional Publication No. 218917/89 (H1218917). In the conventional driving control apparatus of Provisional Publication No. 218917/89, in cases where an output alternating current of an inverter arranged between the battery or the electric power generator and the motor-driven compressor is larger than a limited value, a ratio of an output frequency of the inverter to an output voltage of the inverter is lowered to reduce the output alternating current of the inverter to less than the limited value. Accordingly, the motor-driven compressor is protected from burning out.
3. Problems to be Solved by the Invention
However, because the battery is utilized to supply the electric power to not only the drive motor but also the motor-driven compressor in the electric motorcar, an electric energy stored in the battery is exhausted unless an electric power consumed by the motor-driven compressor is limited in some way. As a result, the electric motorcar stops running before a driver arrives at his destination. Also, because the electric generator is utilized to supply an electric power to the motor-driven compressor in the gasoline car, the electric generator is overloaded unless the electric power consumed by the motor-driven compressor is limited in some way. As a result, the electric generator burns out.
In the conventional driving control apparatus, the electric power supplied to the motor-driven compressor is controlled by detecting only the output alternating current of the inverter. Therefore, though the motor-driven compressor and power transistors utilized to convert a direct current voltage applied by the battery or the electric generator into an alternating current voltage applied to the motor-driven compressor can be protected, the battery or the electric generator is not protected from the exhaustion of the electric power or the overload on the electric generator.